1. Field of the Invention
The present invention relates to a stereoendoscope wherein images having passed through plural incident pupils are transmitted by common relay optical systems so that an observation providing a stereo-feel may be possible.
2. Description of the Related Art
Recently, particularly in the surgical field, there is known a so-called endoscope operation wherein, in order to reduce the burden on the patient, without opening the abdomen, a small hole is made in the abdominal part, and an endoscope is inserted through the hole for the observation and treatment. In this field, the operation has been already made by directly and stereoscopically viewing the affected part with both eyes and therefore, even in the endoscope operation, stereo-inspection is strongly desired. If the stereo-inspection can be made, the operation will be easy, the operation time will be reduced and the hardship on the patient will be further reduced.
As a stereo-inspection endoscope whereby stereo-inspection is possible, there is a first related art example suggested in a Japanese patent application No. 309078/1992 shown in FIG. 1A wherein two identical optical systems are arranged in parallel and the images formed by the objective optical systems 401 and 401' are transmitted for a predetermined distance by the transmitting optical systems 402 and 402' (in this case, relay lens systems) and are taken by such image taking devices 403 and 403' as CCD's.
The taken pair of the right and left images are converted to electrical signals and are displayed in a TV monitor (not illustrated). At this time, when the displayed right and left images are switched at a high speed and simultaneously shutter spectacles synchronized with the images are used, the image for the right eye will be observed with the right eye and the image for the left eye will be observed with the left eye so as to be able to be stereo-inspected.
Also, as another type stereoendoscope, there is a second related art example suggested in a Japanese patent application No. 28278/1993 shown in FIG. 2A wherein the objective optical system 414 and the relay lens system 415 which is a transmitting optical system are formed of one axially symmetrical optical system. A prism 416 is arranged at the rear end of the relay lens system 415 and a pair of right and left images having a parallax are formed and taken in the image taking devices 417 and 417' by spatially dividing the pupil into two with the prism. FIGS. 1B and 2B on the left side of FIGS. 1A and 2A show respective incident pupils.
In order to make a stereo-inspection, it is necessary to obtain a pair of right and left images having a parallax from each other. Therefor, the incident pupil for the right image of the optical system and the incident pupil for the left image must be spatially separated. Also, the magnitude of the stereo-feel in the case of the stereo-inspection is proportional to the center distance between the right and left incident pupils.
In the two above-mentioned related art examples, in the case of the first type in which the same two optical systems are arranged, when the objective optical systems 401 and 401' to the image taking means 403 and 403' are separately formed and the left and right incident pupils 407 and 407' are separately positioned, images having a parallax from each other will be obtained. The center distance d between the left and right incident pupils 407 and 407' coincides with the optical axis distance D between the left and right objective optical systems 407 and 407'.
In the second type in which the pupil is divided among the above-mentioned related art, the objective optical system 414 and transmitting optical system 415 are formed of one axially symmetrical optical system and the pupil is one in this part but, when this one pupil is spatially divided into two by the pupil dividing means (in the above mentioned case, the pupil dividing prism) 416 and respective images are produced, images having a parallax from each other will be obtained. The center distance d between the left and right incident pupils 418 and 418' is 1/2 the size of the incident pupil 419 of the objective lens.
In the type in which the same two optical systems are arranged, as it is formed of separate right and left parts, the number of the parts is high, thereby increasing the difficulty in assembly. Also, the magnification difference between the right and left images due to the errors of the respective parts is large, the displacement of the focusing position is large, the normal stereo-inspection cannot be made and therefore a fine adjustment is necessary.
In the type of dividing pupil, there are advantages that the parts common to the right and left light paths are many, the number of parts is low and the displacement of the right and left images can be made small. On the other hand, when compared with the same thickness, the magnitude of the parallax will be smaller than in the first type and a sufficient stereo-feel will be difficult to obtain. That is to say, there is a problem in that the center distance between the right and left incident pupils is difficult to make large. This point shall be explained with reference to FIGS. 3A to 4B.
FIG. 3A is a magnified view of the objective optical system on the distal end side of the first related art example. FIG. 3B shows its incident pupil. Also, FIG. 4A is a magnified view of the objective optical system on the distal end side of the second related art example. FIG. 4B shows its incident pupil.
In the type in which the same two optical systems are arranged, that is, the first related art example, against the inside diameter .PHI. of the objective lens frame 421 of the endoscope distal end 420, the optical axis distance between the right and left objective optical systems is substantially .PHI./2. Therefore, the center distance between the right and left incident pupils 407 and 407' is also substantially .PHI./2.
On the other hand, in the type in which the pupil is divided, against the inside diameter .PHI. of the objective lens frame 421 at the endoscope distal end 420, the diameter of the incident pupil 419 of the objective optical system is smaller than .PHI., because the incident pupil of the objective optical system is smaller than the pupil of the relay lens system as the NA of the endoscope is limited by the outside diameter of the relay lens system and the picture angle of the objective optical system is larger than of the relay lens system.
Therefore, the center distance between the right and left incident pupils is less then .PHI./2 and is usually about .PHI./6 to .PHI./10. Therefore, in this type, the magnitude of the parallax is about 1/3 that in the above mentioned type. Particularly, when the distal end is thin, no sufficient stereo-feel will be obtained.